1. Field of the Invention
The present invention relates to a flat picture-reproducing device and to a method of operating such a device.
2. Description of the Prior Art
A flat picture-reproducing device is known from an article entitled "Der flache Fernsehbildschirm" published in Vol. 10 (1980) of the Funkscha" periodical, pp. 63 to 66, FIG. 2. FIG. 2 of said article is further explained in a digest of a technical paper by W. Scott, et al, entitled: "Flat Cathode-Ray-Tube Display", SID International Symposium, Digest of Technical Papers, 1978, S.88 and 89. It has a glass faceplate which is at a high positive potential and whose inside is coated with phosphors, a digitally addressed multilayer control arrangement for shaping and modulating the stream of electrons, an area cathode which emits a uniform stream of electrons in the direction of the control arrangement, and a metal-shell vacuum enclosure at the rear. The cathode is formed by a periodic array of oxide-coated heating wires in whose vicinity a field-shaping counterelectrode is located. In a plane between this counterelectrode and the heating wires, a periodic array of elongate field-shaping electrodes arranged parallel to the heating filaments is provided.
This area cathode requires a large amount of heating power because the cathode must provide the maximum current density for the peak brightness at any moment, although only a fraction of the current density is needed most of the time. This static operating mode is detrimental to the oxide-coated heating wires and shortens their useful life. At the same time, the current requirement is increased due to the complicated control arrangement, which is only slightly transparent to electrons.